Ford Ka heater blows only cold, 12volts reaching control valve, both in and out water pipes to heater are hot yet only cold air inside car? can there be any reason other than the control valve?

sounds like the hot cold valve has stuck its behind the wiper panel having 2 pipes in and 2 out and a 12v plug on it check the voltage too this too should be 12v when hot is selected on the heater control panel also carfully feel the pipes if one is really hot and one cold the valve has stuck closed there about £5 from a car breakers not that difficult to change with minimal tools or pay a garage anything from £90 too £150 for the repair.

Check the temp dial, the potentiometer may be faulty

this is a common fault. heater control valve faulty under scuttle pannel how to test .turn heater control switch half way between hot and cold with fan blowing then touch the valve if it is[ pulsing] ticking then faulty 100% sure this is the problem

First you have to identify what causes the problem.
To do this you have to:
1) When engine is cold check the level of coolant. If it is low fill it up.
2) Start engine and check if engine reaches regular temperature. If your engine is not heated enough it means your thermostat does not work properly and should be replaced.
3) If engine temperature is normal, then check the temperature of pipes that go to/from heater core. These pipes are located up the fire wall (easier access is from the passenger side). If pipe/pipes are cold (even engine is worm) it means you heater core is plugged and should be flushed. Keep in mind, flushing the whole cooling system is different from flushing heater core.
4) If pipe/pipes are hot/warm, turn off the fan, switch controller to the hot position, wait for 3-4 minutes and turn on the fan. Note if the cold air blows first or warm air blows first but it cools down in 5-10 seconds. If the air blows cold than it is most probably the problem with blend door or blend door actuator.
5) If air blows warm first and then cools down, then while running engine and remaining the transmission in PARKING position, press on the gas pedal until your engine reaches 3,000 RPM. Check if your heater blows warm/hot air. If it does, then your water pump does not work properly and should be replaced. If the air still cold, I would suggest to flush the heater core.

First you have to identify what causes the problem.
To do this you have to:
1) When engine is cold check the level of coolant. If it is low fill it up.
2) Start engine and check if engine reaches regular temperature. If your engine is not heated enough it means your thermostat does not work properly and should be replaced.
3) If engine temperature is normal, then check the temperature of pipes that go to/from heater core. These pipes are located up the fire wall (easier access is from the passenger side). If pipe/pipes are cold (even engine is warm) it means you heater core is plugged and should be flushed. Keep in mind, flushing the whole cooling system is different from flushing heater core.
4) If pipe/pipes are hot/warm, turn off the fan, switch controller to the hot position, wait for 3-4 minutes and turn on the fan. Note if the cold air blows first or warm air blows first but it cools down in 5-10 seconds. If the air blows cold than it is most probably the problem with blend door or blend door actuator.
5) If air blows warm first and then cools down, then while running engine and remaining the transmission in PARKING position, press on the gas pedal until your engine reaches 3,000 RPM. Check if your heater blows warm/hot air. If it does, then your water pump does not work properly and should be replaced. If the air still cold, I would suggest flushing the heater core.

Theres a door under the dash that directs air over the heater core if it is broken then you will not get heat but you will still have a/c.To fix it you will have to take dash apart.
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sounds like heater control valve situated under scullle panel common fault on ka set heater fan switch half way between hot and cold with heater blowing then touch valve if pulsing or clicking noise it is faulty if doesnt solve problem faulty switch

Your problem is a faulty heater control valve. The design used on these vehicles allows for hot water to flow constantly and compete with the evaporator as there is no blender door. You have to replace the valve and possibly the control head. Meanwhile, you can bypass the valve to have cold air

Taurus does not use a heater control valve. It runs coolant thru the heater core constantly. You may have a temp blend door actuator problem or a plugged up heater core is also very common. Feel the heater hoses, they should both be very hot, it one is much cooler; you can try to back flush the core.

I think you could be right about there being air trapped in the system.
Or the heater core(radiator) is plugged.
Either way you need a pressurized radiator coolant pump to put the coolant in without air being trapped.
Although,i have seen it done by jacking the vehicle up high enough that the radiator was now higher than the heater core level, and then the coolant was put in.
But this is dangerous to try.